This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled A System And Method For Tuning Of Broadcasting Signal Receiver earlier filed in the Korean Industrial Property Office on Sept. 21, 2000, and there duly assigned Serial No. 00-55478 by that Office.
1. Field of the Invention
The present invention relates to an apparatus and method of receiving broadcast signals, and more particularly, to a tuning system and a tuning method in a broadcast signal receiver, in which a radio frequency (RF) spectrum signal adopting an inverting method is filtered by the asymmetric bandpass filter of a tuner to improve the receiving sensitivity.
2. Description of the Related Art
FIG. 1 is an exemplary RF spectrum diagram of a broadcast signal RF spectrum having a structure in which an 8 VSB (8-level vestigial side band) digital broadcast spectrum signal is located in the empty channel between a lower analog NTSC (National Television System Committee) spectrum (hereinafter, referred to as a lower NTSC spectrum) and an upper analog NTSC spectrum (hereinafter, referred to as an upper NTSC spectrum). Also, as shown in FIG. 1, the audio signal of the lower NTSC spectrum is separated by only 0.56 MHz from a pilot tone of the 8 VSB digital broadcast spectrum.
Upon 8 VSB reception, proper detection of a pilot tone is important for signal recovery by a receiver so that it can determine the performance of a receiving unit. An 8 VSB transmission system transmits data using a single pilot tone instead of multiple pilot tones as upon a coded orthogonal frequency division multiplexing (COFDM) of DVB-T. Thus, damage to the pilot tone on a transmission line may prevent proper reception.
In particular, when an 8 VSB digital broadcast spectrum signal is adjacent to an existing is NTSC spectrum, the audio signal of a lower NTSC spectrum is separated by 0.56 MHz from the pilot tone of the 8 VSB digital broadcast spectrum signal. Accordingly, when the lower NTSC spectrum is very large, a pilot tone on the 8 VSB digital broadcast spectrum may be damaged. Also, since the pilot tone of the 8 VSB digital broadcast spectrum is separated by 1.25 MHz from the luminance signal of an upper NTSC spectrum, the interference of the upper NTSC spectrum signal is usually 3-4 dB lower than the interference of the lower NTSC spectrum signal.
Accordingly, if there are no upper NTSC signals, a transmitting unit usually shifts the frequency of an 8 VSB signal by several tens of kHz toward the upper side in order to minimize the interference of a lower NTSC signal. In this case, a receiving unit captures the shifted frequency by automatic fine tuning (AFT) and thus can achieve accurate tuning. However, the receiving unit does not know how much the frequency is shifted, and thus usually sweeps a frequency of about 1.5 MHz based on the central frequency, resulting in time-consuming automatic fine tuning. In recent digital techniques, it takes several minutes to search for the entire channel during initial auto program execution. An 8 VSB transmission method as shown in FIG. 1 provides poor NTSC adjacent-channel characteristics and prolongs the time for a receiving unit to perform automatic fine tuning.
Difficult audition of 8 VSB signals under indoor circumstances and vulnerability to a variety of multipaths are largely affected by the fact that a tuning system uses a single pilot tone in contrast to COFDM. Distortion of the single pilot tone on a transmission line can bring even a situation where reception is impossible. It is no exaggeration to say that the performance of reception of 8 VSB signals can be greatly affected by how well the pilot tone is detected. For example, when a tuner is made up of a symmetrical band pass filter, damage to a pilot tone on a transmission line may have a fatal effect on the carrier recovery by a VSB chip (not shown) at the rear side.
To solve the above problem, an objective of the present invention is to provide a tuning system of a broadcast signal receiver, in which an inverting method for an 8 VSB digital broadcast signal is adopted instead of an exemplary normal spectrum method, and an asymmetric bandpass filter in which a low pass portion has a large gain is included in a tuner of a receiving unit, so that the sensitivity of reception of 8 VSB signals is improved.
An objective of the present invention is to provide a tuning method for a broadcast signal receiver, in which an inverting method for an 8 VSB digital broadcast signal is adopted instead of an exemplary normal spectrum method, and an asymmetric bandpass filter in which a low pass portion has a large gain is included in a tuner of a receiving unit, so that the sensitivity of reception of 8 VSB signals is improved.
The first objective of the present invention is achieved by a tuning system including: a first mixer for mixing a predetermined oscillation frequency with an inverted digital broadcast signal in the idle space between normal upper and lower NTSC broadcast signals of a high frequency band received from a transmitter, transferring the upper NTSC broadcast signal to the lower side and the lower NTSC broadcast signal to the upper side, inverting the transferred NTSC broadcast signals, and changing the state of the digital broadcast signal into a normal state; a filter for attenuating the inverted upper and lower NTSC broadcast signals output from the first mixer to a predetermined band and amplifying the normal digital broadcast signal into a predetermined band; and a second mixer for mixing a predetermined oscillation frequency with the attenuated NTSC broadcast signals and the amplified digital broadcast signal output from the filter and lowering the frequency of the mixed signal to a predetermined frequency band.
The second objective of the present invention is achieved by a tuning method including: (a) transmitting an inverted digital broadcast signal in the idle space between normal upper and lower NTSC broadcast signals of a high frequency band; (b) transferring the upper NTSC broadcast signal to the lower side and the lower NTSC broadcast signal to the upper side, inverting the transferred NTSC broadcast signals, and changing the state of the digital broadcast signal into a normal state; and (c) attenuating the inverted upper and lower NTSC broadcast signals to a predetermined band, and amplifying the normal digital broadcast signal into a predetermined band and lowering the frequency of the amplified digital broadcast signal to a predetermined frequency band.